On Thu, Mar 20, 2014 at 10:45 AM, Tom Lane wrote:
> Robert Haas writes:
>> So you might think that the problem here is that we're assuming
>> uniform density. Let's say there are a million rows in the table, and
>> there are 100 that match our criteria, so the first one is going to
>> happen 1/1
On Thu, Mar 20, 2014 at 8:51 PM, Tom Lane wrote:
> Atri Sharma writes:
> > Now, why cannot we take the estimate of all the buckets behind the bucket
> > in which our value is present? Will that estimate not give us the
> fraction
> > of tuples that are expected to be before the first matching ro
Atri Sharma writes:
> Now, why cannot we take the estimate of all the buckets behind the bucket
> in which our value is present? Will that estimate not give us the fraction
> of tuples that are expected to be before the first matching row?
Uh, no, not unless you assume that the table happens to b
On Thu, Mar 20, 2014 at 8:10 PM, Robert Haas wrote:
> On Tue, Mar 18, 2014 at 2:41 PM, Tom Lane wrote:
> > Atri Sharma writes:
> >> One of the factors that leads to bad estimates is that the histogram of
> the
> >> values of a column maintained by the planner gets old by time and the
> data
> >
Robert Haas writes:
> So you might think that the problem here is that we're assuming
> uniform density. Let's say there are a million rows in the table, and
> there are 100 that match our criteria, so the first one is going to
> happen 1/10,000'th of the way through the table. Thus we set SC =
On Tue, Mar 18, 2014 at 2:41 PM, Tom Lane wrote:
> Atri Sharma writes:
>> One of the factors that leads to bad estimates is that the histogram of the
>> values of a column maintained by the planner gets old by time and the data
>> in the column changes. So, the histogram is no longer a quite accu
Atri Sharma writes:
> One of the factors that leads to bad estimates is that the histogram of the
> values of a column maintained by the planner gets old by time and the data
> in the column changes. So, the histogram is no longer a quite accurate view
> of the data and it leads to bad selectivity
On Tue, Mar 18, 2014 at 11:43 PM, Josh Berkus wrote:
>
> > On Mon, Mar 17, 2014 at 8:47 PM, Tom Lane wrote:
> >> Yeah. I would like to see the planner's cost estimates extended to
> >> include some sort of uncertainty estimate, whereupon risk-averse people
> >> could ask it to prefer low-uncert
> On Mon, Mar 17, 2014 at 8:47 PM, Tom Lane wrote:
>> Yeah. I would like to see the planner's cost estimates extended to
>> include some sort of uncertainty estimate, whereupon risk-averse people
>> could ask it to prefer low-uncertainty plans over high-uncertainty ones
>> (the plans we typicall
